Apparatus and method for stimulating a brain of a person

ABSTRACT

An apparatus for stimulating a brain ( 3 B) of a person ( 2 ) comprising a detector ( 10 ) for detecting an induced or a spontaneous physiological signal generated by the brain ( 3 B), a control unit ( 12 ) being connected to said detector ( 10 ) for comparing the detected physiological signal with a criterion to determine an optimal setting of a variable signal parameter, a first signal generator ( 8 ) for applying an electrical stimulation signal (EES) to said person ( 2 ) and/or at least one second signal generator ( 9 ) for applying a sensory stimulation signal (SSS) to a sensory organ ( 3 A) of said person ( 2 ), wherein a signal parameter of the stimulation signals (ESS, SSS) are adjusted to the determined optimal setting of said signal parameter.

The invention relates to an apparatus and a method for stimulating abrain of a person, in particular via a sensory organ, such as an eye ofthe person, to restore impaired regions of the sensory organ or areas inthe brain that process sensory or other information.

Sensory organs of a person, such as the eyes, the ears or the sense oftouch of a person can be impaired or fail completely. Alternatively,brain structures which process information, both sensory and otherwise,may be impaired following damage. In particular eyes or ears of a personcan be damaged through external influences such as accidents or bydiseases causing an impairment of the respective sensory organ.

FIGS. 1 a, 1 b shows as an example of different types of lesions in thevisual system of the brain and the corresponding type of visual fielddefect VFD of a person. For example, a lesion of the optic nerve of oneeye causes a monocular blindness on this eye as shown in FIG. 1 b.Regions in the visual pathway behind the chiasma, in contrast, result inbinocular vision loss. There are many different visual defects which arecaused by damage of the retina of the eyes, such as macular degenerationand glaucoma.

In the prior art it is known that stimulation of retina cells canproduce phosphenes. U.S. Pat. No. 5,944,747 describes a method ofphosphene generation in retina tissues through deeper intermediateretinal cellular electrical stimulation wherein a stimulating electrodeis positioned in the vicinity of the retinal tissue and a long durationstimulation signal is applied through an electrode such that deeperintermediate retinal cells are preferentially stimulated over retinalganglion cells and proximal overlying surface axons.

Also, the brain can be stimulated directly to produce phosphenes. Thepaper by Gothe et al. (Gothe, J., Brandt, S. A., Irlbacher, K., Röricht,S., Sabel, B. A. and Meyer, B. U. (2002). Changes in visual cortexexcitability in blind subjects as demonstrated by transcranial magneticstimulation. Brain 125: 479-490) describes such an approach.

Further U.S. Pat. No. 5,522,864 describes an apparatus and a method forocular treatment, wherein a first electrode of a direct current sourceis placed in direct electrical contact with an eyelid of a person and asecond electrode of the current source is placed in direct electricalcontact with a skin site of the person so that a direct electricalcurrent can flow between both electrodes at an amplitude of 5-1,000 μAmpfor a predetermined period of time to treat defects of the eye.

Thus, the electrical stimulation by applying an electrical signal withvariable frequencies to a person via electrodes attached to an eye or tothe brain of the person is well known in the prior art. However, in theconventional electrical stimulation methods the electrical stimulationis performed without additional stimulation of the sensory organ such asthe eye by a sensory stimulation signal. Furthermore, the adjustments ofthe signal parameters of the electrical stimulation signal are done byhand in these conventional electrical stimulation methods. Therefore, anapplication of the electrical stimulation signal is both cumbersome andvariable because different operators use different parameter selectioncriteria. Furthermore, the conventional electrical stimulation of asensory organ in the conventional electrical stimulation methods is notlinked to actual sensory functions. This causes an artificialstimulation to the brain of the person comprising a global electricalstimulation without connection in any meaningful way to functionalsensory parameters.

In prior art electrical stimulation methods, the adjustment of thestimulation parameters of the electro-stimulation signal for stimulatinga sensory organ is done manually by an operator without taking intoaccount that each individual, i.e. each person, reacts differently tothe same electrical stimulation signal. In the conventional electricalstimulation methods the operator has to react to the subjective feedbackof the treated person which might indicate whether it does seephosphenes in the treated area of the eye caused by the electricalstimulation signal or not. In response to the information given by thepatient the operator will adjust the parameter of the electricalstimulation signal to find a setting which causes an optimal reaction ofthe patient. For instance, an operator will vary the frequency of apulsed electrical stimulation signal and ask the treated person toindicate when a maximum amount of phosphenes is caused by the electricalstimulation signal. Naturally a manual adjustment of the frequency ofthe employed stimulation signals will take some time and will dependstrongly on the subjective assessment of the treated person and on theperson applying the treatment.

Accordingly, it is an object of the present invention to provide amethod and an apparatus which automatically applies optimal stimulationsignals to a sensory organ of a person or to the brain of the personaccording to a selectable and automatically controllable objectivecriterion.

This object is achieved by an apparatus having the features of mainclaim 1.

The invention provides an apparatus for stimulating a brain of a personcomprising a detector for detecting an induced or a spontaneousphysiological signal generated by the brain, a control unit beingconnected to said detector for comparing the detected physiologicalsignal with a criterion to determine an optimal setting of a variablesignal parameter, a first signal generator for applying an electricalstimulation signal to said person and/or at least one second signalgenerator for applying a sensory stimulation signal to a sensory organof said person, wherein a signal parameter of the stimulation signalsare adjusted to the determined optimal setting of said signal parameter.

In one embodiment of the apparatus according to the present invention,the detected physiological signal is an electroencephalogram (EEG)signal, a magneto-encephalogram signal or a BOLD-signal measured byfunctional magnetic resonance imaging.

In one embodiment of the apparatus according to the present invention,the induced physiological signal is a response to at least onestimulation signal generated by a signal generator, wherein a signalparameter of said stimulation signal is varied.

In one embodiment of the apparatus according to the present invention,the detector is an EEG (electroencephalogram) detector.

In one embodiment of the apparatus according to the present inventionthe signal parameter is the frequency f of the stimulation signal.

In one embodiment of the apparatus according to the present inventionthe criterion is a maximum amplitude of the physiological signal whereinthe optimal setting of the varied frequency f is formed by a resonancefrequency (f_(R)), for example of the EEG-signal. The resonancefrequency f_(R) is that frequency which produces the maximum possibleresponse, for example the maximum possible EEG amplitude.

In one embodiment of the apparatus according to the present inventionthe resonance frequency f_(R) is determined by varying the frequency fof the sensory stimulation signal SSS applied to the sensory organ ofthe person and then selecting that specific frequency which reaches thepredetermined criterion.

In one embodiment of the apparatus according to the present inventionthe sensory stimulation signal SSS is an optical (visual) stimulationsignal, an auditory stimulation signal or a mechanical stimulationsignal (vibration) to excite the sense of touch on the skin surface.

In one embodiment of the apparatus according to the present inventionthe resonance frequency f_(R) is determined by varying the frequency fof an electrical stimulation signal ESS applied to the personautomatically within a predetermined frequency range.

In one embodiment of the apparatus according to the present inventionthe stimulation signal is a sine wave signal.

In one embodiment of the apparatus according to the present inventionthe stimulation signal is a rectangular signal.

In one embodiment of the apparatus according to the present inventionthe frequency f of the stimulation signal is varied automatically in afrequency range between 0-100 Hz to determine a resonance frequencyf_(R) of the electroencephalogram signal (EEG).

In one embodiment of the apparatus according to the present inventionthe determined optimal setting of the signal parameter of the simulationsignal is stored in a memory unit.

In one embodiment of the apparatus according to the present inventionthe control unit is connected to the signal generator via control linesto control said signal generator such that the electrical stimulationsignal ESS and the sensory stimulation signals SSS comprise apredetermined phase relationship.

In one embodiment of the apparatus according to the present inventionthe electrical stimulation signal ESS is applied to the person viaelectrodes wherein at least one electrode is fixed near the sensoryorgan of the person or fixed directly to the skull.

In a further embodiment of the apparatus according to the presentinvention the electrical stimulation signal ESS is applied to the personvia magnetic stimulation coils, wherein at least one stimulation coil isfixed near the sensory organ of the person or directly to the skull ofthe person.

In one embodiment of the apparatus according to the present inventionthe sensory organ is formed by an eye of the person.

In an alternative embodiment of the apparatus according to the presentinvention the sensory organ is formed by an ear of the person.

In one embodiment of the apparatus according to the present inventionthe sensory organ is formed by a touch sensory organ of the person.

In one embodiment of the apparatus according to the present inventionthe optical sensory stimulation signal is formed by a pulsed flash lightgenerated by a light bulb.

In an alternative embodiment of the apparatus according to the presentinvention the optical sensory stimulation signal is formed by an opticalsignal generated by a light emitting diode.

In a further alternative embodiment of the apparatus according to thepresent invention the optical sensory stimulation signal is formed by apredetermined stimulus pattern displayed on a display monitor.

In one embodiment of the apparatus according to the present inventionthe optical sensory stimulation signal is applied to an impaired regionof the visual field of the eye or the brain.

The invention further provides a method according to claim 25.

The invention provides a method for stimulating a brain of a personcomprising the steps of detecting a physiological signal generated bysaid brain, comparing the detected physiological signal with apre-selected criterion to determine an optimal setting of a variablesignal parameter, and applying an electrical stimulation signal and/orat least one further sensory stimulation signal to a sensory organ,wherein the signal parameter of the stimulation signals are adjusted tothe determined optimal setting of said signal parameter.

In the following embodiments of the apparatus and the method accordingto the present invention are described with reference to the enclosedfigures.

FIGS. 1 a, 1 b show different types of visual field defects fordifferent types of lesions;

FIG. 2 shows an embodiment of a stimulation apparatus according to thepresent invention;

FIG. 3 shows a flow-chart for illustrating a possible embodiment of themethod according to the present invention;

FIG. 4 shows a further flow-chart for illustrating a possible embodimentof the method according to the present invention;

FIG. 5 shows an example for a visual field defect VFD of a person;

FIGS. 6 a, 6 b shows an example for the determination of areas ofimpaired vision of a person;

FIGS. 7 a, 7 b show an example for a visual field defect chart and acorresponding signal pattern as employed by an embodiment of theapparatus according to the present invention;

FIGS. 8 a to 8 d show a visual field defect chart VFC and examples forstimulation signals applied to the sensory organ by the apparatusaccording to the present invention.

As can be seen from FIG. 2 a stimulation apparatus 1 according to anembodiment of the present invention is provided for stimulating asensory organ 3A of a person 2 wherein in the embodiment shown in FIG.2, the stimulated sensory organ 3A is formed by an eye of the person 2,wherein each sensory organ 3A stimulates a brain 3B of the person 2

In the embodiment shown in FIG. 2 at least one first electrode 4 isfixed close to or around the eye 3A and a second electrode 5 is fixed tothe skull of the person 2 as a reference electrode. Both electrodes 4,5are connected by signal lines 6,7 to a stimulation signal generator 8generating an electrical stimulation signal ESS. A further sensorystimulation signal generator 9 is provided for generating a sensorystimulation signal SSS which is formed in the embodiment shown in FIG. 2by an optical signal.

A signal detector 10 for detecting an induced or spontaneousphysiological signal is provided. The signal detector 10 is formed, forinstance, by an EEG-detector 10 which detects an electroencephalogramsignal EEG by one or more electrodes which are attached to the skull ofthe person 2. The EEG signal is output via signal line 11 to a controlunit 12. The control unit 12 compares the detected electroencephalogramsignal with a criterion which is input by an operator via an inputdevice 13. The control unit 12 controls the sensory stimulation signalgenerator 9 via a control line 14 and the electrical stimulation signalgenerator 8 via a control line 15. In a first step one of the two signalgenerators 8, 9 or both signal generators 8, 9 apply a stimulationsignal to the person 2, wherein a signal parameter of the respectivestimulation signal such as the frequency f of the stimulation signal isvaried automatically within a predetermined frequency range Δf. Thecontrol unit 12 monitors the measured electroencephalogram signalgenerated by the EEG signal detector 10 and compares the detectedelectroencephalogram signal EEG with the selected criterion to determinean optimal setting of the varied signal parameter.

In other embodiments, the detector 10 detects other physiologicalsignals of the brain 3B such as a magneto-encephalogram signal or aBOLD-signal measured by functional magnetic resonance imaging.

In a possible embodiment the selected criterion is a maximum amplitudeof the physiological signal, e.g. the electroencephalogram signal EEGcaused by a specific frequency of the applied stimulation signals. Inthis embodiment the optimal setting of the varied frequency f is formedby a resonance frequency f_(R) of the detected physiological signal. Atthe resonance frequency f_(R), the physiological signal comprises amaximum amplitude A_(max).

In one embodiment the resonance frequency f_(R) is determined by varyingthe frequency f of the sensory stimulation signal SSS applied to thesensory organ 3A of the person 2 by the sensory stimulation signalgenerator 9.

In an alternative embodiment the resonance frequency f_(R) is determinedby varying the frequency f of the electrical stimulation signal ESSgenerated by the stimulation signal generator 8 within a predeterminedfrequency range Δf. Typically, the electrical stimulation signal ESSapplied to the head of the person 2 is in the range of 0-100 Hzpreferably around 10 Hz and at a current of 0-5.0 mAmp, preferably 0.5mAmp. The signal of the applied electrical stimulation signal ESS can beformed by rectangular pulses or sine wave pulses. The signal pulses areapplied either as single pulses or as pulse trains which consist of manyrepetitive pulses. Furthermore, the shape of the pulse can vary; forinstance, a high amplitude positivity can be followed by a low amplitudebut extended negativity. Preferably, the sum of both equals zero.

In the embodiment shown in FIG. 2 the electrical stimulation signal ESSis applied to a skull of the person 2 via electrodes 4,5. One or severalelectrodes 4 are fixed to the region near the eyeball and the neutralreference electrode 5 is placed on the skull or at the skin of anotherbody part.

In one embodiment of the apparatus according to the present inventionthe electrodes 4,5 are attached directly to the skull of the person 2.

In an alternative embodiment of the apparatus 1 according to the presentinvention the electrical stimulation signal ESS is applied to the person2 by means of magnetic stimulation coils (transcranial magneticstimulation) which are held in position by a holding device.

While stimulating the sensory organ 3A of the person 2 the EEG-signaldetector 10 detects an electroencephalogram signal of the person 2 10can collect information from one or from more than one recordingelectrodes

In a possible embodiment EEG-electrodes are fixed to the skull of theperson and brain-wave-signals are measured preferably as evokedpotentials. The frequency f of the applied simulation signal which mightbe formed by the electrical stimulation signal ESS or by both theelectrical and the sensory stimulation signal is varied in apredetermined frequency range Δf to determine an optimal setting of thefrequency f producing a maximum amplitude A_(max) of theelectroencephalogram signal. This optimum frequency forms the resonancefrequency f_(R) which is stored by the control unit 12 as anEEG-parameter in a memory unit 16 of the stimulation apparatus 1. Eachindividual person 2 has their own individual resonance frequency f_(R)at a given point in time.

In a first operation mode the stimulation apparatus 1 according to thepresent invention is switched to a measuring procedure for determiningthe respective resonance frequency f_(R) of the person 2. The controlunit 12 is switched to this operation mode by the operator by means ofmode control switch 17, as shown in FIG. 2. The stimulation apparatus 1indicates by a display when the resonance frequency f_(R) of the person2 has been found and is stored into memory unit 16.

When the resonance frequency f_(R) of the respective person 2 is foundthe stimulation apparatus 1 switches in one embodiment automatically toanother operation mode wherein the electrical stimulation signal ESS andat least one further sensory stimulation signal SSS are both applied tothe sensory organ 3A with a frequency f that is adjusted to thedetermined optimal setting of the signal parameter, i.e. to theresonance frequency f_(R) of the person 2 stored in the memory unit 16.

In an alternative embodiment the operator switches the stimulationapparatus 1 to the other operation mode when the resonance frequencyf_(R) has been determined.

In one embodiment the stimulation apparatus 1 first records aspontaneous EEG of the person 2, analyzes the actual alpha brain waveactivity and then stimulates with the stimulating electrode 4 a desiredfrequency based on the spontaneous EEG recording. For example, if aperson 2 has a spontaneous EEG alpha activity of 11.0 Hz but thepre-selected frequency target is 10.2 Hz, then the stimulating electrodewill be set at 10.2 Hz until the point where the spontaneous EEG show avalue closer to 10.2 Hz as well.

In one embodiment of the stimulation apparatus 1 according to thepresent invention the stimulation apparatus 1 comprises a phase controlunit which controls a phase relationship between the sensory stimulationsignal SSS and the electrical stimulation signal ESS applied to theperson 2.

In one embodiment the sensory stimulation SSS and the electricalstimulation signal ESS are applied simultaneously to the person 2, i.e.a phase difference Δφ between the two signals is zero.

In a possible embodiment the electrical stimulation signal ESS comprisesa resonance frequency f_(R) of 10 Hz and is applied to the person 2 in asynchronous manner with a 10 Hz visual stimulus signal.

In an alternative embodiment there is predetermined phase difference Δφbetween the two stimulation signals. For instance an electrical pulsetrain is applied to the person 2 via electrodes 4,5 for a duration of 10seconds with a specific frequency and then visual pulses are applied tothe sensory organ 3A of the person 2 at the same frequency f for thenext 10 seconds.

In yet another embodiment, the current strength of the electricalstimulating electrode 4 is varied while the frequency f is heldconstant.

In one embodiment the electrical stimulation signal ESS and the sensorystimulation signal SSS are applied in an alternating manner at apredetermined frequency f.

In one embodiment the electroencephalogram EEG signal is measured with asilver chloride electrode or a gold electrode positioned on the skullwherein the EEG-signal recording can be performed with a singleelectrode or multiple electrodes.

The signal generator 9 generating the sensory stimulation signal SSS isformed in one embodiment by a light pulsed generating a bulb flashlight.

In an alternative embodiment the sensory stimulation signal generator 9generates visual stimulation signals SSS formed by light emitting diodesLEDs.

In a still further embodiment of the stimulation apparatus 1 accordingto the present invention the sensory stimulation generator 9 forgenerating a visual stimulation signal is formed by a display displayinga predetermined visual signal pattern. Such a stimulus pattern can beformed by any pattern useful to produce visual perceptions. A possiblepattern is a moving spiral displayed to the person 2. The visualstimulus can be any kind of stimulus, e.g. a moving pattern or a simplestationary geometric pattern such as a triangle or a square.

FIG. 3 shows a flow chart of possible embodiment of the method accordingto the present invention.

After starting step S0, the control unit 12 operates for determinationof an optimal setting of a variable signal parameter previously set bythe input device. The selected criterion can be a resonance frequency orsome other physiological parameter such as a brain wave frequency, forexample a certain alpha-wave frequency. When the operator has input thecriterion in Step S1, the stimulation apparatus 1 switches in oneembodiment to a first operation mode for determining the optimal settingof the variable signal parameter. In an alternative embodimentstimulation apparatus 1 does not wait for an input of the criterion butautomatically starts its operation by using a preselected criterion.

In step S2, a stimulation signal is applied to the person 2 with avaried signal parameter for instance by changing the frequency f of thestimulation signal in the predetermined frequency range Δf. Thestimulation signal can be formed by the electrical stimulation signalESS or by the sensory stimulation signal SSS or by both signals at thesame time. The stimulation signal can vary by frequency or currentstrength or by a combination of the two.

In a step S3 the detector 10 measures the physiological signal, e.g. aEEG signal, and the control unit 12 determines the optimal setting ofthe varied signal parameter by analysing the generated physiologicalsignal according to the selected criterion.

As soon as the control unit 12 has found the optimal setting of thesignal parameter, e.g. the resonance frequency f_(R) of the person 2this signal parameter is stored in the memory unit 16 in step S4 and thestimulation apparatus 1 switches automatically to another operation modefor restoring impaired regions of the sensory organ 3A. In thisoperation mode the stimulation apparatus 1 applies the electricalstimulation signal ESS and the sensory stimulation signal SSS with theoptimal setting of the signal parameter, i.e. with the setting stored inthe memory unit 16. Both signals ESS, SSS are applied to the person 2with a predetermined phase relationship.

The duration of the application of the electrical stimulation signal ESSand the sensory stimulation signal SSS corresponds to a predeterminedtime span of, for instance, several minutes.

As can be seen from FIG. 4, in one embodiment of the apparatus 1according to the present invention, first, an electrical pulse signal isapplied in a predetermined frequency range of, for example 0 to 100 Hz.

In a further step, alpha amplitudes of the physiological signal aremeasured by an EEG-detector 10. The operator inputs as a predeterminedcriterion a maximum amplitude of the measured physiological signal,wherein in the example of FIG. 4, the point of the maximum amplitude ismeasured at a frequency of 10.8 Hz. This signal parameter, i.e. afrequency of 10.8 Hz is stored in the memory unit 16 of the stimulationapparatus 1 according to the present invention as shown in FIG. 2. Inthe example of FIG. 4, the operator selects stimulation signals to beapplied to the person 2. In the given example, as a first sensorystimulation signal SSS visual stimulation signal is selected and, as asecond stimulation signal an electrical stimulation signal ESS isselected to be applied to the person 2 via electrodes. In a furtherstep, an electrical stimulation of the brain 3B is performed by means ofthe electrical stimulation signal ESS applied to the person 2 viaelectrodes 4, 5. In a predetermined phase relationship as input by theoperator, the visual stimulation of the sensory organ 3A is performed ata frequency of 10.8 Hz being the resonance frequency f_(R) Of the personat this time point.

The electrical stimulation signal ESS and the visual sensory stimulationsignal SSS are coupled to each other. Both signals have a predeterminedphase relationship and they are applied to the person 2 at the samefrequency f of 10.8 Hz. This signal parameter is detected by evaluatingthe physiological EEG-signal according to a predetermined objectivecriterion input by the operator via the input device 13.

FIG. 5 shows an example for a visual field defect chart VFC of an eye ofa person 2 comprising blind regions indicated in black. To determinesuch a visual field defect chart, a simulation signal is presented to aperson 2 by means of a monitor and the patient has to fixate his eyes ata cross shown in the center of FIG. 5. Stimulation signals are presentedat random positions on the monitor and the patient 2 responds to eachstimulus by pressing a key or a response button. When the patient doesnot react this position is stored in the memory as well and subsequentvisual field defect charts which document the patients performance thisposition is represented by a black square in the visual field defectchart VFC as shown in FIG. 5. If a patient reacts properly a whitesquare is accorded to the respective area. The visual field defect chartVFC reveals regions of vision versus areas of blindness.

In most cases patients do not only comprise areas of vision and areas ofblindness but also areas of residual vision which are partially damaged,i.e. the patient sometimes responds to a stimulation signal applied forthis area and sometimes he does not.

FIG. 6 shows a process of how such areas of residual vision aredetermined. At various times T1-TX separate visual field defect chartsare generated and, subsequently, a super-imposed visual field defectchart VFC is generated as shown in FIG. 6 b. This parametric testingreveals areas where the patient 2 responds unreliable to vision stimulishown as grey areas in FIG. 6 b.

In a preferred embodiment of the stimulation apparatus 1 according tothe present invention the visual stimulation signal SSS is applied onlyto damaged areas, i.e. areas of residual vision (grey regions in FIG. 6b) and areas of blindness (black regions in 6 b).

FIG. 7 a shows a parametric visual field defect chart VFC of a patient2. FIG. 7 b shows the regions where a stimulation signal SSS ispresented to the patient 2 having the visual field defect chart of FIG.7 a. The white areas in FIG. 7 b indicate areas of maximum stimulation,grey indicates intermediate stimulation and black areas indicate areasof no stimulation. As can be seen from FIGS. 7 a, 7 b blind areas ofFIG. 7 a receive maximum stimulation as shown in FIG. 7 b.

In a preferred embodiment the greater the deficit of a region of the eyeindicated by the visual field defect chart VFC the greater the amount ofvisual stimulation for this region.

In one embodiment the amount of visual stimulation is increased byincreasing the frequency f of the sensory stimulation signal SSS.

In an alternative embodiment the amount of visual stimulation isincreased by increasing the amplitude of the sensory stimulation signalSSS.

In a preferred embodiment of the stimulation apparatus 1, a control unit12 is connected to a visual field defect chart memory 17 storing thevisual field defect chart VFC of the respective person 2.

The visual field defect chart VFC of the person 2 is loaded to thememory 17 in one embodiment via an interface from a data-carrier.

In an alternative embodiment stimulation signal generator 9 formed by amonitor or a display is provided for performing a perimetric method tocreate the visual field defect chart VFC of the person 2.

In this embodiment, the simulation apparatus 1 is used in a firstoperation phase to create a visual field defect chart VFC of the person2. Then in a second operation phase, the resonance frequency f_(R) ofthe person 2 is determined and in a third phase the sensory organ 3A ofthe person 2 is stimulated by the stimulation signals wherein the amountof stimulation, i.e. the amplitude or frequency, is adjusted in responseto the visual field defect chart VFC of the person 2 stored in thememory unit 16. Accordingly, in this embodiment of the stimulationapparatus 1, a first signal parameter of the stimulation signals SSS,ESS e.g. the frequency f of the stimulation signal is adjusted to theoptimal setting, i.e. to the resonance frequency f_(R) of the person 2,and another signal parameter of the stimulation signals SSS, ESS, e.g.the amplitude is adjusted depending to the VFC visual field defect chartof the person 2 stored in the VFC chart memory 17.

The restoration stimuli signals can be presented from several seconds toa longer time period such as an hour.

FIG. 8 b-8 d show an example of an application stimulation signal to aneye 3A of a person 2 having a visual field defect chart VFC as shown inFIG. 8 a. The visual field defect chart VFC shows different regions ofthe eye showing different degrees of vision. For example, undamagedregions show an ability of 100 percent (white) and completely blindregions show an ability of 0 percent (black). Grey regions in the visualfield defect chart VFC indicate the presence of residual vision of somesurviving neurones. Cells in these residual regions which are partiallydamaged areas of the brain, fire in an asynchronous manner (FIG. 8 b).During electro-stimulation as shown in FIG. 8 c the residual neuronesare activated repetitively at the same time and the evoked potentialcauses phosphenes. By repetitive stimulation of these areas, theresidual vision can be enhanced significantly. This can be seen in FIG.8 b where cells in the damaged areas do not fire in synchronous manner.By application of an electrical simulation signal ESS, the cells firesynchronously to each other. When the electrical stimulation signal ESSand the visual stimulation signal SSS are coupled to each other as shownin FIG. 8 d more cells are expected to fire which will then produce amore intense restoration effect in the brain.

In an embodiment of the stimulation apparatus 1 according to the presentinvention, the apparatus sends stimulation signals SSS as an opticalsensory stimulation signal generated by an optical signal generator suchas a light bulb.

In an alternative embodiment stimulation apparatus 1 according to thepresent invention, the apparatus 1 is provided for stimulating anauditory organ 3A of a person 2, i.e. an ear of the person 2. In thisembodiment, the stimulation signal SSS provided by the sensorystimulation signal generator 9 is an auditory stimulus such as a pulsedtone or click which is systematically sent with different frequencies(pitch) or loudness (in decibel). These stimulation signals can bepresented at random or in a particular order, e.g. ascendingfrequencies. The stimulation apparatus 1 identifies, in a possibleembodiment, auditory deficits on the basis of a criterion to determineparameters of an auditory restoration stimulation signal. For example, atone of x decibel is presented to the person 2 in a frequency range0-100 Hz. If the patient does not respond for instance at frequenciesranging from 20-40 Hz at a given loudness, the sensory stimulationsignal SSS and the electrical stimulation signal ESS are applied to thepatient 2 at this frequency f at the same time or with a predeterminedphase difference.

In a still further embodiment of the stimulation apparatus 1 theapparatus 1 is used for stimulation of somatosensory organs i.e. atouching sensory of the person 2. In this embodiment, the sensorystimulation signal generator 9 is formed by a vibration device placed onthe skin of the person 2. A vibration frequency is systematically variedand with different pressure on the skin. The frequency f of thevibration device is varied at random or in a particular order, forexample, by increasing the vibration frequency. In this manner thesimulation apparatus 1 identifies somatosensory deficits. For example, avibration signal can be presented in a frequency range Δf from 0-100 Hzand then a stimulation signal SSS is selected having a frequency whichcorresponds to the deficient frequency.

In a possible embodiment the deficiencies of the ear or the touch senseis detected automatically by the control unit 12 by evaluating aphysiological signal detected by the detector 10.

In possible embodiments, memories are provided for storing a chart ofthe deficiencies of the respective sensory organ 3A, which can be formedby an ear or by a skin area of the person 2. An acoustic chart of thepatient's ear or a somato-sensory chart of the skin body portion of thepatient is stored in a memory indicating the frequencies of impairedhearing or impaired feeling.

The present invention is useful not only for the treatment of sensorydisorders (such as vision loss, hearing loss or somatosensory loss) butfor other disorders as well because synchrony of brain waves (EEG) asinduced by electro-stimulation with or without sensory coupling mayaffect all disorders where the nervous system is impaired. Thesedisorders comprise: Stroke and head injury, Coma and loss ofconsciousness; neglect, cognitive impairments and dementia afterAlzheimer's Disease; cognitive impairments in normal aging; Parkinson'sDisease, movement disorders as induced by, for example, hemiplegia;Speech disorders, including Aphasia; Memory impairments; deficits inattention and concentration, Multiple Sclerosis, Huntington's Disease,reading impairments including dyslexia, Vision impairments affecting theoptic system and the retina including myopia, glaucoma, maculardegeneration, strabismus, amblyopia, retinitis pigmentosa developmentaldisorders in children; peripheral nerve disorders.

1-25. (canceled)
 26. A stimulation apparatus for stimulating a brain ofa person comprising: a control unit which controls a first signalgenerator to apply a generated electrical stimulation signal to asensory organ of said person and a second signal generator to apply agenerated sensory stimulation signal to the sensory organ of saidperson, wherein in a first operation mode a frequency of the appliedstimulation signal formed by the electrical stimulation signal or byboth, the electrical and the sensory stimulation signal is varied in apredetermined frequency range to determine an optimal setting of thefrequency producing a maximum amplitude of an induced electro- ormagnetoencephalogram signal which is generated by the brain of saidperson in response to the applied electrical stimulation signal or inresponse to the electrical stimulation signal and the sensorystimulation signal and which is detected by a signal detector connectedto said control unit, wherein in a second operation mode the electricalstimulation signal and the sensory stimulation signal are both appliedto the sensory organ with a frequency that is adjusted to the determinedoptimal setting of the frequency forming an individual resonancefrequency of said person.
 27. The stimulation apparatus according toclaim 26, wherein said signal detector is an EEG-detector.
 28. Thestimulation apparatus according to claim 27, wherein said sensorystimulation signal is an optical stimulation signal, and auditorystimulation signal or a vibration stimulation signal.
 29. Thestimulation apparatus according to claim 26, wherein said stimulationsignal is a sine wave signal or a rectangular signal.
 30. Thestimulation apparatus according to claim 26, wherein the frequency ofthe stimulation signal is varied in a frequency range Δf between 0-100Hz.
 31. The stimulation apparatus according to claim 26, wherein thedetermined optimal setting of the frequency of the stimulation signal isstored in a memory unit.
 32. The stimulation apparatus according toclaim 26, wherein said control unit is connected to the signalgenerators via control lines to control said signal generators such thatthe electrical stimulation signal and the sensory stimulation signalcomprise a predetermined phase relationship.
 33. The stimulationapparatus according to claim 26, wherein the electrical stimulationsignal is applied to said person via electrodes or magnetic stimulationcoils wherein at least one of said electrodes or magnetic stimulationcoil is fixed near the sensory organ of said person.
 34. The stimulationapparatus according to claim 33, wherein the sensory organ to which saidelectrode or magnetic stimulation coil is fixed is formed by an eye ofsaid person, by an ear of said person or by a touch sensory organ ofsaid person.
 35. The stimulation apparatus according to claim 28,wherein the optical sensory stimulation signal is formed by pulsed flashlight generated by a light bulb.
 36. The stimulation apparatus accordingto claim 28, wherein the optical sensory stimulation signal is generatedby light emitting diode device.
 37. The stimulation apparatus accordingto claim 28, wherein the optical sensory stimulation signal is formed bya predetermined stimulus pattern displayed on a display monitor.
 38. Theapparatus according to claim 34, wherein the optical sensory stimulationsignal is applied to an impaired region of the eye of said person. 39.The stimulation apparatus according to claim 26, wherein a memory isprovided for storing a sensitivity chart indicating a sensitivity ofareas of the sensory organ to a respective sensory stimulation signal.40. A method for stimulating a brain of a person comprising the stepsof: applying in a first operation mode a stimulation signal which isformed by an electrical stimulation signal or by both, an electrical anda sensory stimulation signal, with a varying frequency to a sensoryorgan of the person, wherein the frequency is varied in a predeterminedfrequency range to determine an optimal setting of the frequencyproducing a maximum amplitude of an induced electro- ormagnetoencephalogram signal generated by the brain of said person inresponse to the applied electrical stimulation signal or in response tothe electrical stimulation signal and the sensory stimulation signal anddetected by a signal detector; and applying in a second operation modean electrical stimulation signal and a sensory stimulation signal to thesensory organ of said person with a frequency that is adjusted to thedetermined optimal setting of the frequency which forms an individualresonance frequency of said person.